Preconception Hair Mercury and Serum Omega-3 Fatty Acids in Relation to Gestational Weight Gain Among Women Seeking Fertility Care

Few studies have prospectively examined the joint effect of mercury (Hg) and omega-3 long-chain polyunsaturated fatty acids on gestational weight gain (GWG). This exploratory study included 120 women from the Environment and Reproductive Health (EARTH) study with preconception measurements of hair Hg and serum eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), followed through pregnancy. Linear regression was used to examine associations between hair Hg and GWG, while logistic regression estimated the odds of inadequate GWG based on National Academy of Medicine recommendations. In unadjusted models, higher hair Hg (≥1 vs. <1 ppm) was associated with lower GWG (β = -1.89; 95% CI: -3.70, -0.08) and increased odds of insufficient GWG (OR = 2.27; 95% CI: 1.00, 5.18). However, after multivariable adjustment including serum EPA + DHA, these associations were attenuated and became non-significant. A negative, though not statistically significant, association between hair Hg and GWG was observed among women in the lowest tertile of serum EPA + DHA (≥1 vs. <1 ppm: β = -3.26; 95% CI: -7.69, 1.17), whereas no such association was observed among those in higher tertiles (β [95% CI] = 0.44 [-4.21, 5.09] and -1.05 [-4.13, 2.02], respectively). Our findings suggest that the association between preconception Hg exposure and insufficient GWG may differ by serum EPA + DHA, but results require confirmation in cohorts with larger sample sizes.